在 C# 中绘制到新“层”

构建一个小绘画程序并尝试合并图层的概念。

我使用 PictureBox 控件来显示图像，并从 PictureBox 显示的图像中获取 Graphics 对象并绘制到该对象。

我的问题是我试图弄清楚如何绘制覆盖在图片框顶部的新 Graphics 对象，并能够获取新绘制的图像without原始图像吸收到图形中。

如果我做类似的事情：

Graphics gr = Graphics.FromImage(myPictureBox.image);
gr.DrawRectangle(blah blah)

...我正在编辑图片框中的原始图像。我想要一种方法来仅捕获正在绘制的新内容作为单独的图像，但仍然将其显示为覆盖在已有内容之上。

有人能指出我正确的方向吗？谢谢！

我会考虑使用透明控件并进行一些修改，以便它可以用作图像层：

http://www.codeproject.com/Articles/26878/Making-Transparent-Controls-No-Flickering http://www.codeproject.com/Articles/26878/Making-Transparent-Controls-No-Flickering

可能是这样的（根据需要进行任何修改）。

class LayerControl : UserControl
{
    private Image image;
    private Graphics graphics;

    public LayerControl(int width, int height)
    {
        this.Width = width;
        this.Height = height;

        image = new Bitmap(width, height);

        graphics = Graphics.FromImage(image);

        // Set style for control
        SetStyle(ControlStyles.OptimizedDoubleBuffer |
                ControlStyles.AllPaintingInWmPaint |
                ControlStyles.UserPaint, true);
    }

    // this function will draw your image
    protected override void OnPaint(PaintEventArgs e)
    {
        var bitMap = new Bitmap(image);
        // by default the background color for bitmap is white
        // you can modify this to follow your image background 
        // or create a new Property so it can dynamically assigned
        bitMap.MakeTransparent(Color.White);

        image = bitMap;

        Graphics g = e.Graphics;
        g.SmoothingMode = SmoothingMode.AntiAlias;
        g.PixelOffsetMode = PixelOffsetMode.HighQuality;
        g.CompositingQuality = CompositingQuality.GammaCorrected;

        float[][] mtxItens = {
            new float[] {1,0,0,0,0},
            new float[] {0,1,0,0,0},
            new float[] {0,0,1,0,0},
            new float[] {0,0,0,1,0},
            new float[] {0,0,0,0,1}};

        ColorMatrix colorMatrix = new ColorMatrix(mtxItens);

        ImageAttributes imgAtb = new ImageAttributes();
        imgAtb.SetColorMatrix(
            colorMatrix,
            ColorMatrixFlag.Default,
            ColorAdjustType.Bitmap);

        g.DrawImage(image,
                    ClientRectangle,
                    0.0f,
                    0.0f,
                    image.Width,
                    image.Height,
                    GraphicsUnit.Pixel,
                    imgAtb);
    }

    // this function will grab the background image to the control it self
    protected override void OnPaintBackground(PaintEventArgs e)
    {
        base.OnPaintBackground(e);
        Graphics g = e.Graphics;

        if (Parent != null)
        {
            BackColor = Color.Transparent;
            int index = Parent.Controls.GetChildIndex(this);

            for (int i = Parent.Controls.Count - 1; i > index; i--)
            {
                Control c = Parent.Controls[i];
                if (c.Bounds.IntersectsWith(Bounds) && c.Visible)
                {
                    Bitmap bmp = new Bitmap(c.Width, c.Height, g);
                    c.DrawToBitmap(bmp, c.ClientRectangle);

                    g.TranslateTransform(c.Left - Left, c.Top - Top);
                    g.DrawImageUnscaled(bmp, Point.Empty);
                    g.TranslateTransform(Left - c.Left, Top - c.Top);
                    bmp.Dispose();
                }
            }
        }
        else
        {
            g.Clear(Parent.BackColor);
            g.FillRectangle(new SolidBrush(Color.FromArgb(255, Color.Transparent)), this.ClientRectangle);
        }
    }

    // simple drawing circle function
    public void DrawCircles()
    {
        using (Brush b = new SolidBrush(Color.Red))
        {
            using (Pen p = new Pen(Color.Green, 3))
            {
                this.graphics.DrawEllipse(p, 25, 25, 20, 20);
            }
        }
    }

    // simple drawing rectable function
    public void DrawRectangle()
    {
        using (Brush b = new SolidBrush(Color.Red))
        {
            using (Pen p = new Pen(Color.Red, 3))
            {
                this.graphics.DrawRectangle(p, 50, 50, 40, 40);
            }
        }
    }

    // Layer control image property
    public Image Image
    {
        get
        {
            return image;
        }
        set
        {
            image = value;
            // this will make the control to be redrawn
            this.Invalidate();
        }
    }
}

如何使用它的示例：

LayerControl lc = new LayerControl(100, 100);
lc.Location = new Point(0, 0);
lc.DrawRectangle();

LayerControl lc2 = new LayerControl(100, 100);
lc2.Location = new Point(0, 0);
lc2.DrawCircles();

LayerControl lc3 = new LayerControl(100, 100);
lc3.Location = new Point(0, 0);
lc3.Image = new Bitmap(@"<Image Path>");

// adding control
this.Controls.Add(dc);
this.Controls.Add(dc2);
this.Controls.Add(dc3);

使用这种方法，您可以拥有多个可以相互重叠的图层（由于它具有透明功能）。

如果您想将其添加到 PictureBox 的顶部，请确保重新排序该控件。 Layer 控件应添加在 PictureBox 控件之前。

// adding control
this.Controls.Clear();
this.Controls.Add(dc);
this.Controls.Add(dc2);
this.Controls.Add(dc3);
this.Controls.Add(PictureBox1);

希望它有帮助。